A known data transmission network is described in Damon W. K. Wong, George Chen, “Optical design and multipath analysis for broadband optical wireless in an aircraft passenger cabin application”, IEEE Transactions on Vehicular Technology, Vol. 57 (6), 3598-3606, November 2008. Multiple light sources are positioned in the ceiling of the aircraft cabin.
This system suffers from a number of disadvantages. Firstly, being in an aircraft cabin the system can only be operated at wavelengths which are safe to the human eye. Secondly, since multiple light sources are provided, this will make the system heavy and difficult to install. Thirdly, the light sources may interfere with each other in an unpredictable way.
Another known data transmission network is described in patent publication WO 02/05459. A central distribution system transmits a signal via optical fibres to local distribution nodes which communicate with user stations using free space optical links.